Animal eggs of many species including those of echinoderms, amphibia, and mammals, have extracellular coats that play an important role in fertilization. Each coat represents a cell surface-anchored extracellular matrix which is elaborated during oocyte maturation, which is directly involved in cell-cell recognition between the egg and the sperm, and which is structurally modified at fertilization in an organized, and apparently stepwise manner, to form a physical barrier to polyspermy. Structural modifications are accomplished by enzymes and structural proteins released by cortical granule exocytosis just after fertilization. In this proposal Dr. Chandler aims to study the structure of the vitelline layer in the sea urchin egg, of the vitelline envelope in the Xenopus laevis egg, and their conversion the fertilization envelopes. To accomplish this he will prepare high resolution platinum replicas of eggs that have been deep-etched. His aims in sea urchin eggs are: 1) to visualize the intermediate stages that occur during transformation of the vitelline layer into the fertilization envelope, 2) to localize the envelope crosslinking enzyme ovoperoxidase, and its binding protein proteoliasin, by immunogold labelling, and 3) to study the mechanism of paracrystalline protein coating during fertilization envelope assembly. His aims in Xenopus laevis eggs are: 1) to visualize formation of the vitelline envelope (VE) during oocyte growth and meiotic maturation, 2) to view modifications of the VE just after fertilization resulting from interactions of cortical granule secretions with the envelope, 3) to identify by immunogold labelling the 69kD and 64kD components of the vitelline envelope which undergo hydrolytic processing at fertilization, and 4) to study the structure and developmental role of the "M" layer, a newly discovered component of the Xenopus fertilization envelope. %%% These studies are the beginning of a longer term goal which is a comparative study of structure-function relationships in the extracellular matrices of the eggs of several species (echinoderms, amphibians, and mammals). These extracellular matrices are important to fertilization in all these species.
